To increase thermal efficiency and specific thrust, advanced gas turbine stages are designed to operate at increasingly higher inlet temperatures. This increase is made possible by advances in materials such as super alloys and thermal-barrier coatings. There are still significant limitations to operating at high temperatures even when super alloys and thermal barrier coatings (TBCs) are used. Consider that a temperature of 3000° F. (1649 C) is desirable for turbine inlet temperatures associated with power generation and a temperature of 3500° F. (1927 C) is desirable for turbine inlet temperatures associated with aircraft. Yet super alloys typically are limited to about 1050-1200 C and TBCs are typically limited to about 140-170 degrees C. above the material they coat. Thus, to achieve the desired turbine inlet temperatures for improve gas-turbine efficiency and specific thrust/power increases better materials and/or better cooling are needed.
Various advances have been made in cooling technology such as advances in cooling technology such as internal, film, impingement, and other techniques. In film cooling there is convective heat transfer in holes. A layer of cooler air or film is formed to insulate hot gas from a metal or thermal barrier coated surface. However, one of the problems with using film cooling is that the film-cooling jets entrain the hot gases and then lift off the surfaces they are attempting to cool.
Thus, although the problems with cooling surfaces associated with gas turbines have been studied and various improvements proposed, problems remain. What is needed is a method for increasing coverage associated with film cooling by minimizing hot-gas entrainment with minimum cooling flow.